The pneumococcal polysaccharide vaccine is recommended as a means of preventing invasive disease in the elderly. We compared responses to the 23-valent polysaccharide vaccine in 46 previously unvaccinated, healthy, institutionalized elderly persons (mean age, 85.5 years) with those in 12 healthy younger adults (mean age, 37 years) by measuring prevaccination and postvaccination serum IgG antibody concentrations (by ELISA), functional antibody activity (by opsonophagocytosis), IgG antibody avidity, and passive protection in mice. Postvaccination IgG antibody concentrations for two serotypes (6B and 19F) of the five studied (4, 6B, 14, 19F, and 23F) were significantly lower in elderly than in younger adults; however, opsonophagocytic activity was significantly reduced for all serotypes in the elderly. Sera with reduced opsonophagocytic activity (titer, <64) correlated with low IgG antibody avidity and protected mice poorly against pneumococcal challenge. In elderly persons receiving polysaccharide vaccination, there was a significant reduction in the functionality of postvaccination antibodies, and this appeared to increase with advanced age.

The prevalence of immunity to Streptococcus pneumoniae in the adult population of the United States is unknown. In the study described herein, military recruits had anticapsular IgG antibody to only 15% of common pneumococcal serotypes, whereas working men and elderly men had IgG antibody to 33% and 34% of the common serotypes, respectively (P < .001). Among eight elderly subjects, the prevalence of IgG antibody to capsular polysaccharides increased from 30% to 78% after pneumococcal vaccination; 6 years thereafter, the rate of positive reactions had declined to 58% and IgG levels had declined substantially. With revaccination, IgG levels returned to within (+/-) 40% of the original postvaccination levels. IgM and IgG antibody appeared or began to increase in titer 6 days after vaccination; the rate and degree of response were the same after the first and second exposures. Since most individuals rapidly develop IgG antibody after colonization by S. pneumoniae and since IgG confers immunity, these data suggest that pneumonia is infrequent among healthy adults not because preexisting immunity is widespread but because--with colonization--an immune response develops rapidly, preceding specific events that might lead to infection. Our findings support recommended vaccination procedures and suggest that wider application in subsets of healthy younger adults should be considered.

Antibody to pneumococcal capsular polysaccharides (PPS) of Streptococcus pneumoniae plays a major role in protecting the host against pneumococcal infection. A variable proportion of healthy adults have antibody to PPS, often in the absence of recognized pneumococcal infection. To determine whether exposure to pneumococci or colonization by pneumococci, or both, stimulates the emergence of antibody to PPS, we studied outbreaks of pneumonia at two military camps. Of the men who were present at a military training camp during an outbreak of pneumonia due to S. pneumoniae serotype 1 but who did not develop pneumonia, 27.8% had IgG antibody to PPS 1, whereas only 3.6% of controls had this antibody. In another outbreak caused by S. pneumoniae serotypes 7F and 8, 35.9% of asymptomatic soldiers who had nasopharyngeal colonization by one of these strains had antibody to the relevant PPS, and another 30.8% who originally did not have antibody developed it within 30 days; thus, 66.7% of these soldiers had antibody to the relevant PPS. These data show that serotype-specific antibody promptly appears following exposure to an outbreak of pneumococcal pneumonia and is probably mediated through acquisition of nasopharyngeal pneumococcal carriage.

The Centers for Disease Control recommends that, because of a greatly increased susceptibility to pneumococcal infection, all persons infected with human immunodeficiency virus (HIV) receive pneumococcal vaccine. Using an ELISA specific for antibody to capsular polysaccharide, a postvaccination antibody was evaluated to five commonly infecting serotypes of Streptococcus pneumoniae. Thirty-nine HIV-infected persons with less than or equal to 500 CD4 cells exhibited significantly fewer responses than did healthy controls; overall, only 46 (24%) of 195 possible responses were positive compared with 45 (75%) of 60 in 12 HIV-infected subjects with greater than 500 CD4 cells and 92 (74%) of 125 in 25 healthy controls (P less than .001). Subjects with less than or equal to 500 CD4 cells responded to a mean of 1.1 antigens versus a mean of 3.8 and 3.7 in those with greater than 500 CD4 cells and controls, respectively (P less than .001). There were no differences between responses in those with less than 200 and those with 200-500 CD4 cells. Within groups stratified by CD4 cell counts, further stratification by clinical status did not reveal significant differences. Since asymptomatic HIV-infected persons with less than 500 CD4 cells show abnormal responses, pneumococcal vaccine should be given when HIV infection is first detected.